Hermetic Sealing Material

ABSTRACT

Sealing materials for use with membrane supports, and in particular to sealing materials that can be used to form a glassy coating on the exterior surface of a membrane support to prevent gases from entering or exiting the support via the support&#39;s exterior walls.

FIELD

The invention is directed to sealing materials for use with membranesupports, and in particular to sealing materials that can be used toform a glassy coating on the exterior surface of a membrane support toprevent gases from entering or exiting the support via the support'sexterior walls.

BACKGROUND

Monolith-type membrane structures using a porous support having an arrayof parallel channels, typically in a cylindrical form, and a gasselective membrane coated on the inner surface of channel walls, offer ahigher surface area packing density than a single-channel tube of thesame diameter, leading to higher permeation flux. This results in adramatic reduction of both the membrane cost per surface area and theengineering costs to assemble large surface areas of membrane modules.The structures can be used to solve significant energy and environmentalproblems; for example, H₂ recovery from waste gas streams, H₂purification from a production gas mixture for fuel cells application,CO₂ capture from flue gas streams for sequestration, and otherseparations. These separation applications often require hightemperature for better separation performance.

When a mixture gas stream to be separated is supplied into the channelsof a monolith ceramic membrane product, it is separated through themembranes coated on the channel walls, and the permeate thereafterpasses through pores of the membranes and pores of the support to flowout to an external space. The surface area of two ends of the supportexposed to the stream, which includes the end flat surface, and theexterior curved surface of the support, have no membrane coating andtherefore need to be sealed with a sealing material in order to preventthe gas stream being treated from entering and passing through theexposed end surface area and then passing through the pores of thesupport and flowing out of the support with no separation occurring. Theseparation function is therefore more efficient with a seal coating onthe end portion of the support. For separation to occur it is necessaryfor the gas stream to enter the open area of the channels and flowthrough the membrane coated channel walls and the outer porous wall ofthe support.

There is a need for hermetic sealing of the exterior surfaces of analumina membrane support structure to prevent gases from entering orexiting the support through the exterior surfaces instead of enteringthe open area of the channels, passing through the membrane coatedchannel walls and exiting through the unsealed walls of the support.

SUMMARY

One embodiment for high temperature application is an as-batchedzinc-alkali-silicate glass composition consisting essentially of in molepercent:

60-70% SiO₂;

12-18% ZnO;

6-10% Na₂O;

6-10% K₂O;

1-4% ZrO₂; and

0.5-2.5% Al₂O₃.

Another embodiment for high temperature application is an as-batchedcalcium silicoborate glass composition consisting essentially of in molepercent:

30-45% B₂O₃;

25-35% CaO;

23-30% SiO₂;

2-6% Al₂O₃; and

1-5% SrO.

One embodiment for low temperature application is an as-batched mixedalkali-zinc-phosphate glass composition consisting essentially of inmole percent:

35-50% ZnO;

25-40% P₂O₅;

5-10% Na₂O;

5-10% K₂O;

1-5% Li₂O;

1-5% MoO₃;

0.5-4% WO₃; and

0.1-4% Al₂O₃.

Another embodiment for low temperature application is an as-batchedtin-zinc-phosphate glass composition consisting essentially of in molepercent:

40-50% SnO;

25-40% P₂O₅; and

15-30% ZnO.

Such glasses address the need for hermetic sealing of the exteriorsurface of an alumina membrane support structure to prevent gases fromentering or exiting the support through the exterior surfaces instead ofentering the open area of the channels, passing through the membranecoated channel walls and exiting through the unsealed walls of thesupport.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one end of an alumina support with a hermetic coatingsealing the end surfaces and outer curved surface of the aluminasupport, according to one embodiment.

DETAILED DESCRIPTION

This disclosure describes a hermetic sealing material in the form of afrit or frit blend, also referred to herein as a “glass sealingmaterial”, used for the hermetic sealing of the exterior surfaces of analumina membrane support structure. The hermetic sealing material may bea glass composition as described herein or a blend of a glasscomposition as described herein and a filler as also described herein.The choice of hermetic sealing material used to seal the exteriorsurfaces of the support depends on the operating temperature of thesupported membrane. The hermetic sealing material can be divided into 2categories: those that form high temperature glassy coatings and thosethat form low temperature glassy coatings. Low temperature glass sealingmaterials are fired at a temperature of under 700° C. to prevent damageto the membrane layers while forming a glassy coating on the support. Inaddition, the low temperature glassy coating should be able to surviveat 600° C. for several hours for post processing steps. High temperatureglass sealing materials can be fired at a temperature of up to 1400° C.to form a glassy coating on the support. As used herein the term“glassy” means an amorphous glass-like coating formed from the hermeticsealing material after firing that may contain crystals that have formedduring the firing process.

The glassy coating materials, formed after firing, described in thisdisclosure are capable of providing non-porous and hermetic seals on theexterior of an alumina membrane support structure. Hermetic is definedas completely sealed against the entry or escape of a gas. They are ableto survive post processing steps such as deposition of other membranelayers. The materials are CTE (coefficient of thermal expansion) matchedto the alumina membrane support structure. The frit should have zeromismatch or be in mild compression, for example, within ±10×10⁻⁷/° C.from the alumina support CTE.

The membrane support structure comprises a flow-through substrate, suchas an alumina honeycomb. The term “flow-through substrate” as usedherein is a shaped body comprising inner passageways, such as straightor serpentine channels and/or porous networks that would permit the flowof a fluid stream through the body. The serpentine channel helps provideturbulent flow through the channels so as to keep the incoming gas mixedduring the separation process. The alumina support has a selectedlength, an inlet end, an outlet end, and a porous outer curved surfacebetween the inlet and outlet ends. The alumina support is in the form ofa flow-through substrate having a plurality of channels with innersurfaces extending from the inlet end to the outlet end. The aluminasupport may have one or a plurality of membrane layers coating the innersurfaces of the channels of the alumina support.

The alumina support can be made according to suitable methods known inthe art, for example, extrusion. Example alumina membrane supportstructures for membrane supports are disclosed in WO2008073417 A3.

The membrane layers comprise films or porous layers on the interiorwalls of the channels. The membranes may be organic or inorganicdepending on the application. Examples of inorganic membranes andmethods of making them are disclosed in WO2008106028 A1, US 20080299349A1, US 20080299377 A1, and US 20090000475 A1.

FIG. 1 illustrates one embodiment 10 of an alumina support with ahermetic coating sealing the end surfaces and outer curved surface ofthe alumina support; the alumina support 20 is in the form of ahoneycomb substrate. The alumina support 20 has a plurality of channels14, two end surfaces 12 (only one end surface is illustrated in FIG. 1),an uncoated porous curved outer surface 18 b, a hermetic coating 16 aapplied to the end surfaces 12, and a hermetic coating 16 b applied tothe outer curved surface 18 a of the support for a selected distance, L,from the end surface 12 (resulting an a coated outer curved surface 18a). A fitting 22 and a seal 24 (located at both ends of support 20) areused to contain the gas stream 30 entering the alumina support. Thehermetic coating 16 a, 16 b seals the end surface 12 and a selectedlength, L of the coated outer curved surface 18 a of the alumina support20. The hermetic coating 16 b extends a distance from the end surface 12to create a sealed outer curved surface from the end surface 12 to theseal 24. The outer curved surface 18 b in the center region of thesupport between the seals 24, located on both ends of the aluminasupport, is uncoated. The gas stream 30 enters the fitting 22 and entersthe alumina support 20 through the open channels 14. The gas stream 30cannot pass through the porous outer surface of the alumina support inthis region from either direction (outside to inside or inside tooutside) due to the hermetic coating. The gas travels through a distanceto extend past the hermetically coated regions 16 a, 16 b, and seal 24.The gas may travel through the open channel, down the channel wall or acombination of both. A retentate gas 34 continues its path through theopen channels 14 while a permeate gas 32 passes through the membranelayers, alumina support walls, and uncoated outer curved surface 18 b ofthe alumina support 20.

For a high temperature application, in one embodiment, azinc-alkali-silicate glass, combined with high levels (25-50 wt %) ofinert fillers, for example, alumina and/or stabilized zirconia, can beutilized. Zircon may also be used as inert filler. Inert fillers do notreact with the components of the glass composition. Because theas-batched glass is too fluid at the intended 1400° C. firingtemperature to provide hermeticity, inert fillers are blended with theglass to increase the glass viscosity at 1400° C.

The glass compositions given here are on an as-batched basis. Thetransitional phrase “consisting essentially of” limits the scope of aclaim to the specified materials or steps “and those that do notmaterially affect the basic and novel characteristic(s)” of the claimedinvention. That is, as used herein the transitional phrase “consistingessentially of” means that the glass compositions or methods recitedherein contain the specified elements, steps or ingredients as indicatedand excludes additional elements, steps or ingredients which wouldmaterially affect the basic and novel characteristics of the glass,which are that the glass of the compositions of the invention can bemade into a hermetic sealing material.

The glasses can include contaminants as typically found in commerciallyprepared glass. For example, while the glass may comprise zero molepercent barium on an as-batched basis (that is zero barium is added)analysis may find that the glass contains 0.05 mole percent or less ofbarium due to contamination. Such glass is considered herein as being“substantially free” of barium because the source of the barium iscontamination of the batch starting materials. The same is true forarsenic and antimony. While the glass contains zero mole percent arsenicor antimony on the as-batched basis these elements may also be presentin the glass due to contamination. Contamination levels are less than0.05 mole percent. Thus, as with barium, glass composition found tocontain arsenic and antimony are considered as being substantially freeof these materials because their presence arises from the contaminationof the starting materials and they are not intentionally added.

Two glass compositions are disclosed for the high temperature coatingapplications. One embodiment for high temperature application is anas-batched zinc-alkali-silicate glass composition consisting essentiallyof in mole percent:

60-70% SiO₂;

12-18% ZnO;

6-10% Na₂O;

6-10% K₂O;

1-4% ZrO₂; and

0.5-2.5% Al₂O₃.

Another embodiment for high temperature application is an as-batchedzinc-alkali-silicate glass composition consisting essentially of in molepercent:

62-67% SiO₂;

14-16% ZnO;

7-9% Na₂O;

7-9% K₂O;

2-4% ZrO₂; and

0.5-2% Al₂O₃.

Another embodiment for high temperature application is an as-batchedcalcium silicoborate glass composition consisting essentially of in molepercent:

30-45% B₂O₃;

25-35% CaO;

23-30% SiO₂;

2-6% Al₂O₃; and

1-5% SrO.

Another embodiment for high temperature application is an as-batchedcalcium silicoborate glass composition consisting essentially of in molepercent:

36-40% B₂O₃;

27-31% CaO;

24-26% SiO₂;

3-5% Al₂O₃; and

1-4% SrO.

To create a hermetic seal on the outside of the alumina membrane supportstructure for low temperature applications, low glass transition (T_(g))glass fits (T_(g)<350° C.) such as mixed alkali-zinc-phosphate ortin-zinc-phosphate glasses can be utilized. The relatively low T_(g)frits from these glasses can be fired in the 500°-700° C. range to formhermetic coatings. These glasses typically have CTE values around100×10⁻⁷/° C., but this can be adjusted to match the CTE of the aluminamembrane support, about 70-80×10⁻⁷/° C., by adding inert fillers, forexample, beta-eucryptite (Li₂O.Al₂O₃.2SiO₂), beta-quartz orbeta-spodumene.

One embodiment for low temperature application is an as-batched mixedalkali-zinc-phosphate glass composition consisting essentially of inmole percent:

35-50% ZnO;

25-40% P₂O₅;

5-10% Na₂O;

5-10% K₂O;

1-5% Li₂O;

1-5% MoO₃;

0.5-4% WO₃; and

0.1-4% Al₂O₃.

Another embodiment for low temperature application is an as-batchedmixed alkali-zinc-phosphate glass composition consisting essentially ofin mole percent:

40-44% ZnO;

31-35% P₂O₅;

7-9% Na₂O;

6-8% K₂O;

2-4% Li₂O;

2-4% MoO₃;

1-3% WO₃; and

0.5-2% Al₂O₃.

Another embodiment for low temperature application is an as-batchedtin-zinc-phosphate glass composition consisting essentially of in molepercent:

40-50% SnO;

25-40% P₂O₅; and

15-30% ZnO.

Another embodiment for low temperature application is an as-batchedtin-zinc-phosphate glass composition consisting essentially of in molepercent:

42-46% SnO,

31-35% P₂O₅, and

20-24% ZnO.

The mole percents of the components of the glass compositions describedherein are calculated on an oxide basis. The ranges of components in theglass composition comprise, in mole percent, any value includingdecimals in the range, for example, the range for SiO₂ includes 60-70percent SiO₂ for instance 60-65 percent, for example 60.1-64.3 percent.

The glass are batched, melted, and cooled; after cooling they are groundto about 10-15 um/−325 mesh. Optionally and where necessary, inertfillers are added to the glass on a weight basis as necessary to eitherincrease or decrease the CTE of the glass. Examples of fillers includezirconia, alumina, zircon, beta-eucryptite, beta-quartz, andbeta-spodumene. For example, zirconia can be used to increase the CTE ofthe glass, while beta-eucryptite can be used to decrease the CTE of theglass. The blend of glass and filler is also referred to herein as afrit blend. The frit blend may comprise up to 8 wt %, up to 10 wt %, upto 12 wt %, up to 15 wt %, up to 20 wt %, up to 22 wt %, up to 25 wt %,up to 50 wt %, up to 55 wt % filler with the remainder of the frit blendbeing a glass composition as described in paragraphs [0020], [0021],[0022] [0023], [0025], [0026], [0027], or [0028]. The resulting fritblends are sieved through a 325 mesh screen. For high temperatureapplications, the frit blend may contain from 10 wt % to 60 wt % filler,preferably from 15 wt % to 50 wt % filler. For low temperatureapplications, the frit blend may contain from 0 wt % to 25 wt % filler.In some embodiments fillers are not necessary.

The frit blends are combined with suitable liquid vehicle and binder,for example, an amyl acetate vehicle and nitrocellulose binder. Thepaste can then be applied to the exterior of the membrane supportstructure using any suitable technique known in the art, for example,dip coating or air brushing. Depending on the application, the“fluidity” of the paste can be adjusted by varying the amount of liquidused to make the paste. For example, a paste for air brushingapplication may require more liquid than a paste for dip coatingapplication.

One or a plurality of coatings of the hermetic sealing material may beused to minimize the possibility of leakage after sealing, for example 2coatings, 3 coatings, 5 coatings, 8 coatings or 10 or more coatings.Surface roughness of the support may affect the efficiency of thesealing. For example, a rough surface may require more coatings of thehermetic sealing material than a smooth surface. Surface roughnessand/or porosity of the support allows the hermetic sealing material toadhere to the support surface easily.

In some embodiments, drying is required between and/or after coatingapplications. Some embodiments require firing between coatingapplications and after final application. Typically, if 1-2 layers ofhermetic sealing material are applied then only one firing cycle may beneeded. If more than 2 layers of hermetic sealing material are applied,multiple firing cycles may be necessary. In all cases a firing step isrequired after the final layer of hermetic sealing material is applied.The firing temperatures vary according to whether the frit blend is ahigh temperature blend or a low temperature blend. Low temperatureblends may be fired at a temperature of up to about 600° C., or up toabout 700° C. High temperature blends may be fired at a temperature ofup to about 1000° C., or up to about 1400° C. The support with hermeticsealing material coated thereon may be fired at a temperature of about600° C., about 700° C., about 1000° C., or about 1400° C.

In some embodiments, the hermetic sealing material is applied to analumina support and fired before the membrane layers are applied. Inother embodiments, the hermetic sealing material is applied to analumina support that comprises one or a plurality of membrane layers onthe channel walls. If the hermetic sealing material is applied to analumina support comprising one or a plurality of membrane layers, themembrane layers should be able to withstand the temperatures requiredfor firing the hermetic sealing materials without degradation.

After firing the coating forms a glassy material that seals the surfacesto which it has been applied. When heated to a selected temperature thecoating adheres to the exterior surface of the alumina support,hermetically sealing the surface to prevent ingress or egress of fluid.

Also described herein is a method for sealing exterior porous surfacesof an alumina support. The method comprising the steps of providing analumina support optionally comprising a membrane; providing a hermeticsealing material; applying the hermetic sealing material to the ends ofthe channel wall surfaces and the outer curved surface of the supportfor a selected distance from the ends of the support; and firing thesupport having hermetic sealing material thereon.

EXAMPLES

Table 1 shows exemplary as-batched composition, in mole percent, of aglass used for a high temperature coating application. The glasses weremelted in a covered platinum crucible at 1400° C. for 4 hours and thenground to about 10-15 microns/−325 mesh. The d50 (50% of particles arebelow this size) for glass A was 13 microns and 10 microns for glass B.Inert fillers were added to the glasses to increase the viscosity at1400° C. Table 2 shows the frit blend compositions, on a weight basis,for the high temperature coatings. The frit blends were put in a Nalgenecontainer, rolled with alumina balls for 20 minutes, and then sievedthrough a 325 m screen.

TABLE 1 As-batched composition of glass in mole percent used for hightemperature hermetic sealing material. Oxides Glass A Glass B SiO₂ 64.325 Na₂O 8.1 0 K₂O 8.1 0 ZnO 15.3 0 ZrO₂ 2.9 0 Al₂O₃ 1.3 4 SrO 0 3 CaO 029.5 B₂O₃ 0 38.5

TABLE 2 Frit blend compositions in weight percent for high temperaturehermetic sealing material. Materials Frit blend 1 Frit blend 2 Fritblend 3 Glass A (−325 mesh) 50 50 0 Glass B (−325 mesh) 0 0 85 Zircon(ZrO₂•SiO₂, 50 25 0 Aimtek Inc.) A3000 (α-Al₂O₃, Alcoa) 0 25 0 Castabilized ZrO₂ 0 0 15

Three different frit blends of glass A, glass B and filler were made forthe high temperature application. Thin pastes of frit blends 1 and 2were made using an amyl acetate vehicle and nitrocellulose binder.Alumina membrane supports were hand-dipped into the pastes of frit blend1 or 2 and then fired on the following schedule: RT to 1000° C. at 5°C./min, 1000° C. to 1400° C. at 2° C./min, hold at 1400° C. for 1 hourthen cool to RT at 5° C./min Several of the samples coated with onelayer of hermetic coating material were then dip coated a second timeand re-fired at the same schedule. The coatings were glossy with nonoticeable pores extending to the alumina membrane support surface.

A thin paste was made of frit blend 3 using an amyl acetate vehicle andnitrocellulose binder. Alumina membrane supports were air brushed usingthe paste of frit blend 3. The supports were air brushed with 2 layersof frit blend 3 paste, and then fired at 800° C. for 1 hour. Afterfiring they were airbrushed again with 2 additional layers of frit blend3 paste and fired a second time at 800° C. for 1 hour. The coatedsupports had a glossy brown appearance with no cracking or pin holespresent in the coating.

The coated supports were then tested for leakage using a test system ofSwagelok® fittings, along with 2 o-rings to provide a seal with thefittings. The test conditions used were a flow of 2000 sccm of N₂introduced to the system. Only the permeate valve was opened to a wettest meter. The system was allowed to come to equilibrium and the gasflow was measured if any existed. Results after testing show that all ofthe samples with only one coating of hermetic sealing material containsome leakage. Results for the samples coated with two layers of fritblend 1 or 2 show no leaks at more than 150 psi. The results are shownin Table 3.

TABLE 3 Leak test results for high temperature coating application fritblends. Leak Rate System pressure Sample # Description (cc/min) (psi)Frit blend 1 1X coating 20 153 Frit blend 1 2X coating 0 156 Frit blend2 1X coating 73 149 Frit blend 2 2X coating 0 159 Frit blend 3 2Xcoating 62 80 Frit blend 3 4X coating 0 159

Table 4 shows exemplary as-batched composition, in mole percent, of theglasses used for the low temperature application. Glass C is analkali-zinc-phosphate frit and glass D is a tin-zinc-phosphate frit. Theglasses were melted in silica crucibles at 1000° C. for 1 hour. Theywere then poured on a steel table and allowed to cool to roomtemperature. The glasses were then ground to a particle size of about10-15 microns. The specific d50 (50% of particles are smaller than thissize) for glass C was 16 microns and 10 microns for glass D. The CTE forglasses C and D is in the range 90-110×10⁻⁷/° C., a beta-eucryptitefiller (Li₂O.Al₂O₃.2SiO₂) having a CTE of about −10×10⁻⁷/° C., was usedat different loading levels to lower the CTE of the glass C resulting infrit blends 4 and 5. No blends were made using glass D. Table 5 showsthe compositions of the low temperature frit blends. The frit blendswere combined on a weight basis, rolled slowly in a Nalgene bottle withalumina balls for 20 minutes, and then sieved through 325 m screen. Thinpastes were made of frit blends 4 and 5 using an amyl acetate vehicleand nitrocellulose binder. The frit blends were air brushed onto thealumina membrane supports by applying two air brush coatings and thenfiring the supports at 600° C. for 1 hour using a 2° C./min ramp rate.The supports were then coated with 2 additional air brushed layers andfired a second time at 600° C. for 1 hour using a 2° C./min ramp rate.This process was repeated for up to 6 and 8 layers total. One supportcoated with each frit blend 4 and 5 were also fired at a top temperatureof 700° C. for 1 hour using 2° C./min ramp rate to determine if a higherfiring temperature would help increase the flow of the material andthere by yield a more uniform and non-porous coating.

TABLE 4 As-batched composition of glass in mole percent used for lowtemperature hermetic sealing material. Oxides Glass C Glass D Na₂O 8.300 K₂O 7.0 0 ZnO 41.6 22.3 Al₂O₃ 1.0 0 SnO 0 44.7 P₂O₅ 33.4 33.0 Li₂O3.70 0 WO₃ 2.0 0 MoO3 3.0 0

TABLE 5 Frit blend compositions in weight percent for low temperaturehermetic sealing material. materials Frit blend 4 Frit blend 5 Glass C80 90 (16 μm, −325 mesh) β-eucryptite 118VTC 20 10 (+3/−7 μm)

The coated supports were then tested for leakage using the same testapparatus and settings as described above for the high temperaturematerials. The results of the leak testing are shown in Table 6. Thesupport with 8 coating layers of frit blend 5 was hermetic and passedthe leak testing.

TABLE 6 Leak test results for low temperature coating application fritblends. Leak System Blend # or OD Length rate pressure Glass (mm) (mm)Coating process (cc/min) (psi) Frit blend 4 9.9 60 4X coated, 700° C.-1hr 1390 0.95 Frit blend 4 9.8 60.3 4X coated, 600° C.-1 hr 1393 1.3 Fritblend 4 9.5 52.8 8X coated, 600° C.-1 hr 1352 2.7 Frit blend 5 9.7 47.128X coated, 600° C.-1 hr 0 27.7 Frit blend 5 9.7 49.5 4X coated, 700°C.-1 hr 181 27.45 Frit blend 5 9.7 55.3 4X coated, 600° C.-1 hr 86 27.6Glass D 9.6 49.5 4X coated, 600° C.-1 hr 65 27.6

It should be understood that while the invention has been described indetail with respect to certain illustrative embodiments thereof, itshould not be considered limited to such, as numerous modifications arepossible without departing from the broad spirit and scope of theinvention as defined in the appended claims.

Unless otherwise indicated, all numbers used in the specification andclaims are to be understood as being modified in all instances by theterm “about,” whether or not so stated. It should also be understoodthat the precise numerical values used in the specification and claimsform additional embodiments of the invention.

1. A zinc-alkali-silicate glass consisting essentially of, in molepercent: 60-70% SiO₂; 12-18% ZnO; 6-10% Na₂O; 6-10% K₂O; 1-4% ZrO₂; and0.5-2.5% Al₂O₃.
 2. A zinc-alkali-silicate glass according to claim 1,consisting essentially of, in mole percent: 62-67% SiO₂; 14-16% ZnO;7-9% Na₂O; 7-9% K₂O; 2-4% ZrO₂; and 0.5-2% Al₂O₃.
 3. Azinc-alkali-silicate glass according to claim 1, wherein the glass issubstantially free of heavy metals.
 4. A zinc-alkali-silicate glassaccording to claim 1, wherein the glass is substantially free of barium.5. A frit blend comprising 40 to 60 weight percent of thezinc-alkali-silicate glass according to claims 1 and 40 to 60 weightpercent of inert filler.
 6. The frit blend according to claim 5 appliedto an alumina support, where the CTE of the frit blend matches the CTEof the alumina support within ±10×10⁻⁷/° C.
 7. The frit blend accordingto claim 5, where the frit blend is substantially free of heavy metals.8. A calcium silicoborate glass consisting essentially of, in molepercent: 30-45% B₂O₃; 25-35% CaO; 23-30% SiO₂; 2-6% Al₂O₃; and 1-5% SrO.9. A calcium silicoborate glass according to claim 8, consistingessentially of, in mole percent: 36-40% B₂O₃; 27-31% CaO; 24-26% SiO₂;3-5% Al₂O₃; and 1-4% SrO.
 10. A calcium silicoborate glass according toclaim 8, wherein the glass is substantially free of heavy metals.
 11. Acalcium silicoborate glass according to claim 8, wherein the glass issubstantially free of barium.
 12. A frit blend comprising 75 to 95weight percent of the calcium silicoborate glass according to claims 1and 5 to 25 weight percent of inert filler.
 13. The frit blend accordingto claim 12 applied to an alumina support, where the CTE of the fritblend matches the CTE of the alumina support within ±10×10⁻⁷/° C. 14.The frit blend according to claim 12, where the frit blend issubstantially free of heavy metals.
 15. A mixed alkali-zinc-phosphateglass consisting essentially of, in mole percent: 35-50% ZnO; 25-40%P₂O₅; 5-10% Na₂O; 5-10% K₂O; 1-5% Li₂O; 1-5% MoO₃; 0.5-4% WO₃; and0.1-4% Al₂O₃.
 16. A mixed alkali-zinc-phosphate glass according to claim15, consisting essentially of, in mole percent: 40-44% ZnO; 31-35% P₂O₅;7-9% Na₂O; 6-8% K₂O; 2-4% Li₂O; 2-4% MoO₃; 1-3% WO₃; and 0.5-2% Al₂O₃.17. A mixed alkali-zinc-phosphate glass according to claim 15, whereinthe glass is substantially free of heavy metals.
 18. A mixedalkali-zinc-phosphate glass according to claim 15, wherein the glass issubstantially free of barium.
 19. A frit blend comprising 70 to 95weight percent of the mixed alkali-zinc-phosphate glass according toclaim 15 and 5 to 30 weight percent inert filler.
 20. The frit blendaccording to claim 19 applied to an alumina support, where the CTE ofthe frit blend matches the CTE of the alumina support within ±10×10⁻⁷/°C.
 21. The frit blend according to claim 19, where the frit blend issubstantially free of heavy metals.
 22. A tin-zinc-phosphate glassconsisting essentially of, in mole percent: 40-50% SnO, 25-40% P₂O₅, and15-30% ZnO.
 23. A tin-zinc-phosphate glass according to claim 22,consisting essentially of, in mole percent: 42-46% SnO, 31-35% P₂O₅, and20-24% ZnO.
 24. A tin-zinc-phosphate glass according to claim 22,wherein the glass is substantially free of heavy metals.
 25. Atin-zinc-phosphate glass according to claim 22, wherein the glass issubstantially free of barium.
 26. A frit blend comprising 80 to 100weight percent of the tin-zinc-phosphate glass according to claims 1 and0 to 20 weight percent inert filler.
 27. The frit blend according toclaim 26 applied to an alumina support, where the CTE of the frit blendmatches the CTE of the alumina support within ±10×10⁻⁷/° C.
 28. The fritblend according to claim 26, where the frit blend is substantially freeof heavy metals.